The invention relates to a torsion device of an exoprosthesis, with a proximal part which, counter to the action of a resilient torsion element, can be turned in positive and negative directions of rotation in relation to a distal part, the torsion element having, in the positive direction of rotation, a torsion characteristic different than that in the negative direction of rotation.
Shock absorbers are used in exoprostheses for cushioning and absorbing the ground reaction forces. During walking, running or jumping, ground reaction forces caused by ground contact act via the prosthesis and the shaft on the stump and on the rest of the body. Cushioning and absorption of this loading of the sensitive stump and body can help to reduce stump problems, to avoid overloading of the muscles and skeletal apparatus and to improve patient comfort. In the case of above-knee amputees, the rotation capacity of the device compensates for the lack of rotation capacity of the hip joint as a result of the rigid stump-shaft connection at the pelvis. Here, the internal rotation of the foot relative to the pelvis during the stance phase of a walking cycle is of particular importance. In field studies, an increased rotational rigidity (locking moment or initial moment) for small excursions of the shock absorber is considered by patients as very pleasant and stabilizing.
The torsion device described at the outset can be gathered from DE 196 37 173 A1. The latter discloses a prosthesis pylon with a compressible fluid volume contained therein for supporting the weight of a patient. This pylon includes a first end portion which can be secured to the leg stump of the patient, and a second end portion which lies opposite the first end portion and can be connected to a prosthetic foot and can turn relative to the first end portion about a longitudinal axis of the pylon. The first end portion and second end portion are coupled via a torsion spring which with a first spring rate resists a rotation in the clockwise direction and with a second spring rate resists a rotation in the counterclockwise direction, which second spring rate is chosen such that it is chosen differently from the first spring rate depending on whether the leg stump of the patient is a right or left leg stump.
The object of the invention is to improve the functionality of the torsion device described at the outset.
Starting from the torsion device described at the outset, this object is achieved, according to the invention, by the fact that the torsion element comprises two separate torsion spring elements which have different spring characteristics and are each fitted, with prestressing, between their associated abutments in such a way that in each case only one of the two torsion spring elements is active in one of the two directions of rotation, namely only in the positive direction of rotation or only in the negative direction of rotation.
In this definition of the invention, and also in the description which follows, the proximal part could also represent a distal part and the distal part could represent a proximal part; and a torsion spring element could also include a group of torsion spring elements.
The term xe2x80x9cresilientxe2x80x9d is intended to cover elastic and/or viscoelastic and/or friction-adhering spring elements and a viscoplasticity.
In a special embodiment, the two torsion spring elements can be formed by two ring segments which are made of an elastomer and which, viewed in the direction of rotation, bear directly or indirectly on a carrier of the proximal part and on an abutment fixed in a stationary position on the distal part.
To achieve a compact embodiment and a reliable function, it is advantageous if the two torsion spring elements bear with their respective first end on circumferentially opposite sides of the abutment and bear with their respective second end on a respective second abutment, these second abutments being mounted on the distal part in such a way that they can each be displaced in the circumferential direction by at least several circumferential degrees relative to the torsion spring element bearing on them.
To adapt the characteristics to the requirements of the patient, it is expedient for the torsion spring elements to be exchangeable.
In a further embodiment, it is expedient if the second abutments are mounted so as to be displaceable in the circumferential direction in such a way that in each case only one of these abutments can be displaced relative to the torsion spring element bearing on it, while the other second abutment remains held, with prestressing, by a further abutment. This solution results in a markedly high initial rigidity.
According to the invention, the rotation properties of the torsion device can thus be adapted individually, e.g. in terms of internal and external rotation. The different torsional rigidities that can be set thus afford the possibility of permitting a xe2x80x9csoftxe2x80x9d internal rotation and of obtaining more stability by means of a xe2x80x9chardxe2x80x9d external rotation during heel contact and toe take-off. An important factor in terms of the stability felt by the patient is that there is no appreciable rotation under slight torsional moments. The action of the torsion spring elements, dependent on the direction of rotation, which can be achieved according to the invention permits, in conjunction with their prestressing, the creation of a locking moment which is likewise dependent on the direction of rotation.
Since, in addition to the loading caused by torsional moments, axial forces also act in a shocklike manner on the exoprosthesis and the human apparatus of locomotion, it is advantageous if the torsion device is combined with a shock absorber system which has an axial spring element which bears with its distal end on the distal part and bears with its proximal end on the proximal part guided telescopically in the distal part.
Further features of the invention are the subject of the dependent claims and are explained in greater detail, together with further advantages of the invention, with reference to an illustrative embodiment.